Most machine tools, such as gear shapers, which utilize a reciprocating spindle in a cutting stroke and a return stroke are mechanically operated, generally by a crank or by a rack and pinion. These mechanical drive structures must be designed with relatively great strength to withstand the cutting forces, and thus the drive mechanisms are usually heavy and cumbersome.
The speed at which such spindles can operate is usually dictated by the cutting tool. That is, the cutting tool can remove material from the workpiece only during the cutting stroke, and at the start of the return stroke which is usually performed on the second half cycle of one crank revolution, the cutting tool is moved away from engagement with the workpiece so as to avoid damage to its cutting edge. The return stroke thus represents lost time during machine operation, and in conventional machines, about half of the total operating time of the machine is lost time.
Further, while the conventional mechanically driven spindles can be operated at fairly high rates of speed, cutting tool life limits such speed of operation. That is, tool wear in a cutting operation such as is performed in a gear shaper increases alarmingly with increases in cutting velocity. For example, if the reciprocation of a spindle which has been operated at a reasonable rate is doubled, the life of the cutting tool may be quartered.
Accordingly, it is the general object of the present invention to provide a hydro-mechanically operated spindle for a gear shaper or the like which eliminates the heavy and cumbersome drive components of mechanically operated shapers and which will provide precise control for the speed of both the cutting and return strokes of the spindle so that the return stroke can be speeded up and reduce "lost time" and so that the cutting stroke can be controlled to extend tool life at present rates of production or to maintain the present tool life at higher rates of production.